I'm doing some work on a friend's focus before his mot. His airbag light is on, with the flashing code 4-2 on ignition. By doing some research I've localised that code to the LH satellite airbag sensor, but can't find any indication on the internet of where this sensor is.
I found the front one just behind the bonnet latch, and have given that a clean as there was some corrosion on the points, but can someone help me find the offending sensor?

It would appear that there is only one airbag sensor on the front of the car and is mounted to one side of the bonnet lock unit.

The sensor feeds to the control module which determines whether any impact is hard enough to fire the airbags.

The airbag central control module is under the centre console directly in front of the handbrake.

The first thing I'd recommend though is to get the fault codes read and go from there, you may well find that reading and clearing any codes cures the problem.

If not then I'd suspect a wiring fault to the control module or a loose plug.

Do make sure that if you choose to work on the module or any airbag/connections that you disconnect the battery, and leave the car to disperse static for 10 to 20 minutes first to ensure you don't get any accidental bag deployment, and if you do remove any bags that you place them face up in a safe area and never point them at your face/chest or run any power through the bags while disconnected.